July 17, 2008Scientists and engineers are preparing the European Space Agency's Mars Express for several close flybys of the martian moon Phobos. Passing within 100 kilometers of the surface, Mars Express will conduct some of the most detailed investigations of the moon to date.

The series of flybys will take place between July 12 and August 3. During the second encounter, the spacecraft will fly within 273 km of the surface. Mars Express will close to within just 97 km 6 days later.

Although the Red Planet itself has been studied in detail, very little is known about the origins of the moons, Phobos and Deimos. It is unclear if the moons are actually asteroids that were captured by Mars' gravity and never left its orbit. Another possibility is that Phobos and Deimos are actually surviving planetesimals, bodies that formed the planets of the solar systems. They may also be remnants of an impact of a large object on Mars.

As Mars Express closes in on Phobos, the data gathered will help scientists answer these questions.

Mars Express has flown close to Phobos in the past, but this is the first time that the spacecraft will be less than 100 km from the moon. To achieve this proximity to Phobos, spacecraft operations engineers and scientists have been working together to optimize the trajectory of Mars Express to obtain optimum science results&#8212this is not the case for routine flybys.

Mars Express was launched on June 2, 2003, and after releasing the Beagle 2 lander toward the surface, went into orbit around the Red Planet on December 25, 2003.

European Space Agency

As it flies at a distance of 97 km, Mars Express will image areas of Phobos that have never been glimpsed before. The High-Resolution Stereo Camera (HRSC) on board the orbiter will take pictures of the moon's surface y calculating its topography, or the elevation of its surface.

The camera may also capture an image of the intended landing site for Russia's Phobos-Grunt mission, due for launch in 2009. The maneuvers required to observe this site are an operational challenge, and the activity involves close cooperation between ESA mission scientists, the flight control team, and flight dynamic specialists.

The Visible and Infrared Mineralogical Mapping Spectrometer (OMEGA), the Planetary Fourier Spectrometer (PFS), and the Ultraviolet and Infrared Atmospheric Spectrometer (SPICAM) will also gather details on the surface composition, geochemistry, and temperature of Phobos.

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) will collect information during the flybys and July 23 and 28.

The Energetic neutral atoms analyzer (ASPERA) will study the environment around Phobos, in particular the plasma that surrounds the moon and also the interaction of the moon with the solar wind.

During the second flyby, all efforts will be concentrated on accurately determining the mass of the moon using the Mars Radio Science experiment (MaRS).